Research On Thermal Stratification And Temperature Fluctuation In Surge Line Of Pressurized Water Reactor

In nuclear power plant,the thermal stratification and temperature fluctuation will occur in surge line during normal condition and the start-up condition.High-cycle fatigue may take place in the pipe suffering from the temperature fluctuation and the safety of the nuclear power plant may be threatened.So the investigation of the temperature field and the phenomenon of thermal stratification and temperature fluctuation in the surge line is of great value.The phenomenon of thermal stratification in surge line has already aroused wide attention.While,related experimental study is limited due to the complex flow of high-temperature high-pressure fluid.On the other hand,in spite of lots of present numerical simulations,the reliability of the computation has not been fully demonstrated due to lack of relevant experimental results.Base on the present study on thermal stratification and temperature fluctuation,the experimental and the simulative methods were both conducted to study the fluid temperature field in AP1000 surge line in this paper.Details are as follows.At first,the low-temperature and low-pressure test bench was set up and the development of thermal stratification in nuclear power plant was reoccurred.We found mode of rising-up of temperature is different in different part of the surge line.Then,the geometric model was built for the test bench and the simulation was operated using Large Eddy Simulation.The reliability of the simulation method was confirmed through the comparison between the experimental and the simulative results.In addition,we found that the periodical waving of the interface between the cold and hot fluent,which will lead to symmetrical distribution of temperature fluctuation intensity in the same cross section.At last,similar simulations were conducted in AP1000 surge line under the heating-up condition and the normal condition and the relative thermal stratification was studied.We found that the thermal stratification range was 20.7D from the inlet of the surge line under the normal condition and extends to 52 D under the heating-up condition.Besides,temperature difference reached as large as 15 K in the same cross section along the surge line during heating-up period.